Separation and purification of anthracene



Aug. 16, 1955 x.. D. KLElss ETAL 2,715,647

SEPARATION AND PURIFICATION oF ANTHRACENE Filed June 30, 1952 |40 60 |80 TEMPERATURE a F.

@j METHYL A FURFURAL 9 sToDDARD soLvl-:N l

soLUB|L|TY cURvEs, CRUDE ANTHRAcl-:NE N vARnous ORGANK: soLvENTs 8 2 S S 2 8 a 9 m .LNSA'IOS lm 00| Nl CIEAIOSSIG SWVHD INVENTORS L.; D. KLElss By s. J. MARWIL /ULHM a- ATTORNEYS United States Patent O SEPARATION AND PURIFICATION oF ANTHRACENE Louis D. Kleiss and Stanley J. Marwil, Borger, Tex., as-

signors to Phillips Petroleum Company, a corporation of Delaware Application June 30, 1952, Serial No. 296,466

8 Claims. (Cl. 2641-675) This invention relates to the separation and puriiication of crystallizable derivatives of tar. ln one of its aspects this invention relates to the separation and purification of anthracene from the anthracene oil cut in the distillation of coal tar. ln another of its aspects this invention relates to an improved solvent for the crystallization of anthracene in the presence of carbazole, phenanthrene and other components contained in the anthracene oil cut in coal tar distillation.

Anthracene is an aromatic organic compound having the empirical formula C14H1o. amounts, approximately one per cent, in coal tar. it is also found in the residue from the distillation of cracked petroleum products.

Anthracene as a chemical has many uses but its most important use is as a starting point in the making of alizarin, alizarin dye stuffs, and aniline dye stuffs. lt is also used as a reagent in making eniulsiiied insecticidal and fungicidal preparations. It is also an ingredient of lacquers, paints, varnishes, clopes and enamels containing various simple esters of cellulose, such as cellulose acetate and nitrocellulose, or various mixed esters of cellulose such as cellulose acetopropionate (added for the purpose of increasing the life of the film by the absorption of ultra-violet rays). Anthracene is also an ingredient of printing ink used for printing on bank notes, checks and other iiscal papers, secret numbers and marks which are rendered visible by the action of ultra-violet light rays and rays from an X-ray lamp.

As stated, an important source of anthracene is coal tar. Crude coal tar is distilled and the anthracene oil cut, boiling in the range between 572 to 662 F. is collected. This cut, which represents approximately nine per cent oi the original crude coal tar, contains fiuorene, phenanthrene, anthracene, carbazole, and other unidentied components. Anthracene is present in this fraction to the f extent of about l to l5 per cent. On cooling of the anthracene oil cut, the distillate crystallizes to form a crude cake which may be separated from the oily constituent by centrifuging, lter pressing or other means. The conlposition of the cake which is referred to as crude anthracene, depends upon the efficiency and method of operation of the still, and the concentration of the anthracene in said cakes has ranged from approximately up to 35 per cent. The usual procedure for the further concentration of anthracene involves recrystallization from a selective solvent. The most common solvents employed for this purpose are furfural and pyridine, and homologues of each. Solvent naphtha has also been commonly used. ln order to obtain anthracene of 8O to 90 per cent purity, which is the minimum necessary for further use of the anthracene, it is necessary to employ a series of crystallization steps from the solvents.

We have now discovered a superior solvent from which to crystallize anthracene, comprising a monoalkyl ether of diethylene glycol containing from one to four carbon atoms in the alkyl group marketed under the trade-names CarbitoL included among which are methyl Carbitol,

It is found in very small 25,715,647 Patented Aug. 16, 1955 Carbitol (monoethyl ether) and butyl Carbitol. A chief drawback in the use of furfural as such a solvent for crystallizing anthracene is its tendency to form a black polymer, particularly at elevated temperatures. This means that furfural must be used at low temperatures, not above 140 F., lest the polymer formed blackens the anthracene product and renders it unsuitable for dye manufacture. At these low temperatures large volumes of furfural will be used per unit of yield (4 to 6 times as much as in the case of methyl Carbitol, where only the boiling point of the solvent is a limit), and yield will be low unless the anthracene is precipitated under refrigerated conditions. Further, any furfural mother liquor adhering to the anthracene product has to be removed by ushing with another solvent or by high vacuum drying to avoid high temperatures. Also furfural in storage becomes blackened and must be puried before use.

The disadvantages of pyridine (and its homologues) include cost, which is twice as much as in the case of methyl Carbitol; it is a tertiary amine, exhibiting the chemical reactivity common to amines. This leads to high solvelt loss. Further, the odor of pyridine is piercing and objectionable, and it is diiiicult to handle.

It is an object of this invention to provide an improved process for the separation and pu'rication of crystallizable derivatives of tar.

Another object of this invention is to provide an inlproved process for the separation and purification of anthracene from crude anthracene comprising phenanthrene, carbazole and fluorene as impurities.

A further object of this invention is to provide an improved solvent for the crystallization of anthracene in the presence of phenanthrene, carbazole, and other impurities.

Other objects and advantages of this invention will be apparent to those skilled in the art from the accompanying disclosure and discussion.

The accompanying drawing is a graphical presentation and comparison of data.

Our invention resides in the discovery that a solvent comprising a monoalkyl ether of diethylene glycol containing from one to four carbon atoms in the alkyl group commonly known by the trade name Carbitol has superior selective solvent action for anthracene when mixed with other impurities including phenanthrene and carbazole. Methyl Carbitol, a preferred solvent, which is the monomethyl ether of diethylene glycol, is a relatively inert, water-white, hygroscopic liquid of agreeable odor, completely miscible with most organic solvents and with water. It is neutral, stable in storage, stable toward most chemicals and stable toward heat. Since it is heat stable it can be recovered in compact, inexpensive solvent recovery systems. It is also moderate in cost. While methyl Carbitol has been suggested as a solvent for a wide variety of compounds including dyes, oils, fats, waxes, many natural and synthetic resins, nitrocellulose and cellulose acetate, no suggestion has been found in the prior art of the use of methyl Carbitol or compounds of this type in the purification of anthracene.

This invention involves, in a preferred embodiment, dissolving crude anthracene in a solvent comprising diethylene glycol monomethyl ether, cooling the resultant solution to crystallize therefrom anthracene crystals of improved purity and recovering said crystals from the mother liquor. More specifically, we have found that if a crude anthracene containing at least 25 weight per cent anthracene is dissolved in methyl Carbitol and the resultant solution cooled, anthracene crystals of at least per cent purity can be recovered in one crystallization step. Anthracene of still greater purity can be obtained by employing more than one crystallization step,

Itis also possible to employ methyl Carbitol in admixture with other solvents.

, While the present inventionY can be applied to other ,puriiications, it Vwillfoe described in a few specific Y examples,

more particularly in connection with the YVpuriiication of crude anthracene. The following examples are not intended to limit our invention unduly but to aid indescribing itand to aid those skilled in the 'art to practice it.- lso, the advantages of our solvent over the conventional furfural solvent in the purification of anthracene are y aptly demonstrated.

Spectroanalysis: Weight per cent Anthracene n 27.9 Carbazole V n 10.9

VPhimminent V v 23.8

i Example 1 A solution containing ll.4 grams of crude anthracene perV 100 m1. of methyl Carbitol solvent at a temperature Y of'l83" F.'was cooled over a period of two hours to 60 F.

YThe crystal precipitate formed was separated from the mother liquor and the crystals were hot water washed and vacuum dried at 230 F. to remove methyl Carbitol. The-'yield of precipitate on a washed and dried basis was 22.9 per cent. 'The precipitate contained4 81.3 weight per cent anthracene and 0.9 per c ent carbazole. YThe yield'of anthracene obtained was 66.7 per cent.

Example 2Y Fresh distilled furfural was used to avoid deposition of polymer on the precipitate andthe discoloration'fthereof. A solution containing 22.5 grams of crude anthracene .per 100ml. of Vfurfural solvent at 180 F. (which is too Y hot for satisfactory commercial use of furfural as dis "cusscd hereinabove) Wasrcooled to v50 The'precipL tate Vobtained Ywas separated from the mother liquor by 'filtration andV washed with NazSzOs solution andV then Vwashed with water and vacuum dried at 230 F.V to remove furfural. The yield vof'precipitate on a washed and dried basisl obtained was 29.5 per cent. This precipitate contained 75.7 `Weight percent a'nth'rac'ene, 4.5 per centcar- ',.bazol'e, and 4.2 per cent phenanthrene and represented -anthracene'yield of 80 per cent.

Y Y Example 3 fA-solutioncontainin'g `12.4 grams yof crude anthracenc 75 F. VThe crystalline precipitate 'obtained was 'separated Y Vfromv the mother liquor by iiltration -and washed with pentane to remove occluded Stoddard solvent. The precipitate was then oven dried at 210 F. The yieldY of precipitate obtained von a washed and dried basiswas 33.6%. This precipitate 4contained -59.6 per cent anthracene, Y23.0 per cent carbazole and 2.5 per cent phenan- `t hrene, vand represented a 71.7 per cent yield of anthracene.

It kcan thus be seen Vfrom vthe foregoing examplethat -anthracene of greater than 80`.per cent purity can 'be obtained in VV'a single crystallization s'te'p Vby employing 'methyl CarbitolV as a solvent for "the crude anthracene.

Referring to the drawing, heavyjsolid lines 'show lthe -:grams/of crude anthracene Vemployed that completely `dissolve, k100 ml. of solvent at ajgiven temperature. Y

Dotted liners 'show behavior of partially dissolved crude anthracene. The total amount. of crude anthracene presf ent is shown by the ordinate of the intersection ofV a solid and a dotted line. At the temperature indicated by the abscissa of the intersection, all of this crude antiiracene is soluble; as the temperature is lowered, the less soluble components will crystallize out. the amount still in the solution, follow the dotted line to the intersection of the temperature of cooling.` The ordinate` at this point will represent grams of Vmaterial still in solution. Grams precipitated (purified anthracene) may be-obtained by difference.

Example: Assume grams of crude anthracene in 100 ml.'of methyl Carbitol solvent. The heavy solid line for methyl Carbitol .shows that this amount of crude anthracene will completely dissolve at 233 F. On cooling this solution to 80 F. (follow the dotted line to the left) it is found that 23.5 grams will-remain in solution; therefore, 11.5 grams of the more pure anthracenc are precipitated.V Y Y Y Those skilled in the art willreadily appreciate thatV diierent solution and precipitation temperatures can be used in employing our improved solvent for the crystallization and purification of anthracene without departing from the spirit and scope of our invention.

We claim: Y Y

1. A process for the separation and purification of anthracene which comprises, dissolving crude anthracene in a solvent comprising a monoalkyl ether of diethylene glycol containing from one to four carbon atoms in the alkyl group, cooling the resultant solution to crystallize therefrom anthracene crystals of improved purity, and recovering said crystals from the mother liquor.

2. A process according to claim 1 wherein a solvent comprising diethylene glycol monomethyl ether is employed.

3. A process for the separation and purification of Yan thracene which comprises, dissolving crude anthracene in a solvent comprising diethylene glycol monomethyl ether,l cooling the resultant solution to crystallize therefrom anthracene crystals of improved purity, Yrecovering said crystals from the mother liquor, re-dissolving 'saidV crystals in ay further amount of said solvent, cooling the Y second resultant'solution to crystallize therefrom anthracene crystals of still greater purity, and recovering said 'crystals from the mother liquor.

4. A process for the separation and purification of anthracene` which comprises dissolving crude anthracene in a solvent consisting essentially VofV vdiethylene glycol monomethyl ether, cooling the resultant solution to'crystallize therefrom anthracene crystals of improved purity, and recovering said crystals from the mother liquor.V

5. A process for the separation and purification 4of anthracene which comprises, dissolving crude anthra'cene containing at least twenty-five weight per cent anthracene in a solvent consisting essentially of diethylene glycol per 100 ml. ofV Stoddard solvent at 230 F. was cooledto tallize therefrom anthracenecrystals of at least weight per cent purity, Vand Yrecovering 'said crystals from the mother liquor.

Y6. A process for the separation 'and 'purification Vof anthracene which comprises, dissolving crude anthracene obtained Yfrom tar and containing atleast 25 weight per cent athrace'ne in a solvent consisting essentially of diethylene glycol monomethyl ether at a temperature Within Y therange of 175 kto 350 F., cooling .the resultant soluvtion to crystallize ltherefrom anthracene crystals of at least 8O weight .per cent purity, and recovering said crystals from the mother liquor.

7. A process according tol claim l wherein a Vsolvent comprising diethylene glycolV monoethyl Vether is employed. j Y

8. A `process according to claim'l wherein a -solvent comprising diethylene glycol monobutyl ether is employed.

(References on following page) References Cited in the le of this patent UNTTED STATES PATENTS Jaeger Dec. 4, 1928 Cislak Sept. 27, 1932 Jaeger et a1 Sept. 27, 1932 Henderson May 9, 1933 Durrum Sept. 17, 1946 6 OTHER REFERENCES Ind. Eng. Chem., vol. 36, pages 1096-1104 (1944), article by Francis. 

1. A PROCESS FOR THE SEPARATION AND PURIFICATION OF ANTHRACENE WHICH COMPRISES, DISSOLVING CRUDE ANTHRACENE IN A SOLVENT COMPRISING A MONOALKYL ETHER OF DIETHYLENE GLYCOL CONTAINING FROM ONE TO FOUR CARBON ATOMS IN THE ALKYL GROUP, COOLING THE RESULTANT SOLUTION TO CRYSTALLIZE THEREFROM ANTHRACENE CRYSTALS OF IMPROVED PURITY, AND RECOVERING SAID CRYSTALS FROM THE MOTHER LIQUOR. 